Kin selection promotes the evolution of social behavior that increases the survival and reproductive success of close relatives. Among primates, maternal kinship frequently coincides with a higher frequency of grooming and agonistic aiding, but the extent to which paternal kinship influences adult female social relationships has not yet been investigated. Here, we examine the effect of both maternal and paternal kinship, as well as age proximity, on affiliative interactions among semifree-ranging adult female rhesus macaques, Macaca mulatta. Kinship was assessed by using both microsatellites and DNA-fingerprinting. Our study confirms that the closest affiliative relationships characterize maternal half-sisters. We provide evidence that adult females are significantly more affiliative with paternal half-sisters than with nonkin. Furthermore, paternal kin discrimination was more pronounced among peers than among nonpeers, indicating that age proximity has an additional regulatory effect on affiliative interactions. We propose that kin discrimination among cercopithecine primates emerges from ontogenetic processes that involve phenotype matching based on shared behavioral traits, such as inherited personality profiles, rather than physiological or physical characteristics. Kin selection promotes the evolution of social behavior that increases the survival and reproductive success of close relatives (1, 2). Hamilton (ref. 1, p. 22) proposed that one possible mechanism mediating kin selection could be ''familiarity of appearance. . . being [that] relatives must tend to look alike. . . ''. Kin discrimination can arise if individuals classify relatives on the basis of shared family traits (3, 4), i.e., phenotype matching, or if individuals identify relatives on the basis of frequent association patterns (5, 6), i.e., familiarity, but whether these two mechanisms are mutually exclusive or overlapping is unclear (7).Evidence of kin discrimination has been reported for a variety of vertebrate species, e.g., Cascades frog tadpoles, Rana cascadae (8), long-tailed tits, Aegithalos caudatus (9), house mice, Mus musculus (10), white-footed mice, Peromyscus leucopus (11), spiny mice, Acomys cahirinus (12), Belding's ground squirrels, Spermophilus beldingi (3, 13), beavers, Castor canadensis (14), golden hamsters, Mesocricetus auratus (15), and chimpanzees, Pan troglodytes (16). Although most studies of kin recognition have focused on the discrimination of kin versus nonkin, only a few have been able to distinguish paternal half-siblings from nonkin, e.g., Belding's ground squirrels (17), peacocks, Pavo cristatus (18), and savanna baboons, Papio cynocephalus (19). Although Wu et al. (20) concluded that pigtailed macaques, Macaca nemestrina, exhibit kin recognition in the absence of familiarity, based on their finding that unfamiliar juvenile peers prefer to sit closer to their paternal half-siblings than to nonkin, all subsequent studies of cercopithecine primates have failed to replicate the original findings (21-24), which ...

As gut capacity is assumed to scale linearly to body mass (BM), and dry matter intake (DMI) to metabolic body weight (BM(0.75)), it has been proposed that ingesta mean retention time (MRT) should scale to BM(0.25) in herbivorous mammals. We test these assumptions with the most comprehensive literature data collations (n=74 species for gut capacity, n=93 species for DMI and MRT) to date. For MRT, only data from studies was used during which DMI was also recorded. Gut capacity scaled to BM(1.06). In spite of large differences in feeding regimes, absolute DMI (kg/d) scaled to BM(0.76) across all species tested. Regardless of this allometry inherent in the dataset, there was only a very low allometric scaling of MRT with BM(0.14) across all species. If species were divided according to the morphophysiological design of their digestive tract, there was non-significant scaling of MRT with BM(0.04) in colon fermenters, BM(0.08) in non-ruminant foregut fermenters, BM(0.06) in browsing and BM(0.04) in grazing ruminants. In contrast, MRT significantly scaled to BM(0.24) (CI 0.16-0.33) in the caecum fermenters. The results suggest that below a certain body size, long MRTs cannot be achieved even though coprophagy is performed; this supports the assumption of a potential body size limitation for herbivory on the lower end of the body size range. However, above a 500 g-threshold, there is no indication of a substantial general increase of MRT with BM. We therefore consider ingesta retention in mammalian herbivores an example of a biological, time-dependent variable that can, on an interspecific level, be dissociated from a supposed obligatory allometric scaling by the morphophysiological design of the digestive tract. We propose that very large body size does not automatically imply a digestive advantage, because long MRTs do not seem to be a characteristic of very large species only. A comparison of the relative DMI (g/kg(0.75)) with MRT indicates that, on an interspecific level, higher intakes are correlated to shorter MRTs in caecum, colon and non-ruminant foregut fermenters; in contrast, no significant correlation between relative DMI and MRT is evident in ruminants.

The maximum attainable body size of herbivorous mammals: morphophysiological constraints on foregut, and adaptations of hindgut fermenters AbstractAn oft-cited nutritional advantage of large body size is that larger animals have lower relative energy requirements and that, due to their increased gastrointestinal tract (GIT) capacity, they achieve longer ingesta passage rates, which allows them to use forage of lower quality. However, the fermentation of plant material cannot be optimized endlessly; there is a time when plant fibre is totally fermented, and another when energy losses due to methanogenic bacteria become punitive. Therefore, very large herbivores would need to evolve adaptations for a comparative acceleration of ingesta passage. To our knowledge, this phenomenon has not been emphasized in the literature to date. We propose that, among the extant herbivores, elephants, with their comparatively fast passage rate and low digestibility coefficients, are indicators of a trend that allowed even larger hindgut fermenting mammals to exist. The limited existing anatomical data on large hindgut fermenters suggests that both a relative shortening of the GIT, an increase in GIT diameter, and a reduced caecum might contribute to relatively faster ingesta passage; however, more anatomical data is needed to verify these hypotheses. The digestive physiology of large foregut fermenters presents a unique problem: ruminant-and nonruminant-forestomachs were designed to delay ingesta passage, and they limit food intake as a side effect. Therefore, with increasing body size and increasing absolute energy requirements, their relative capacity has to increase in order to compensate for this intake limitation. It seems that the foregut fermenting ungulates did not evolve species in which the intake-limiting effect of the foregut could be reduced, e.g. by special bypass structures, and hence this digestive model imposed an intrinsic body size limit. This limit will be lower the more the natural diet enhances the ingesta retention and hence the intake-limiting effect. Therefore, due to the mechanical characteristics of grass, grazing ruminants cannot become as big as the largest browsing ruminant. Ruminants are not absent from the very large body size classes because their digestive physiology offers no particular advantage, but because their digestive physiology itself intrinsically imposes a body size limit. We suggest that the decreasing ability for colonic water absorption in large grazing ruminants and the largest extant foregut fermenter, the hippopotamus, are an indication of this limit, and are the outcome of the competition of organs for the available space within the abdominal cavity. Our hypotheses are supported by the fossil record on extinct ruminant/tylopod species which did not, with the possible exception of the Sivatheriinae, surpass extant species in maximum body size. In contrast to foregut fermentation, the GIT design of hindgut fermenters allows adaptations for relative passage acceleration, which explai...

One of the basic tenets of sexual selection is that male reproductive success should be large in polygynous species. Here, we analysed 6 years of molecular genetic data from a semi-free-ranging population of rhesus macaques (Macaca mulatta), using Nonac's B index, to assess the level of male reproductive skew in the study troop. On average, the top sire in each year produced 24% of the infants, while 71% of troop males sired no offspring at all. Consequently, 74% of infants had at least one paternal half-sibling in their own birth cohort. Reproductive success was greatest for high-ranking males, males who spent the whole mating season in the troop and males of 9-11 years of age. Heterozygosity for major histocompatibility complex (MHC) class II gene DQB1 was the strongest single predictor of male reproductive success. A negative relationship suggestive of female mate choice was noted between the B index and the proportion of extragroup paternities. Reproductive skew was not associated with relatedness among potential sires or with female cycle synchrony. We conclude that reproductive skew in male rhesus macaques is best accounted for by the 'limited-control' model, with multiple factors interacting to regulate individual reproductive output.